1. Technical Field
The present invention relates to an ink circuit, as well as to an ink jet machine and a conditioning machine or a conveyor using such a circuit.
2. Prior Art
A prior art device is described in U.S. Pat. No. 4,862,192. This device is an ink jet point printer, with an ink circuit incorporating a device for the transfer of thick ink from a first supply tank and, independently thereof, additives from a second supply tank, into an ink chamber. Ink from said ink chamber is supplied under pressure to a writing head. Ink is returned to the ink chamber through a recovery channel, traversing the writing head and recovering the ink droplets which have not been deflected for writing purposes. The transfer device uses pressurized air for transporting the ink between an ink tank connected to the writing head, a mixture tank connected to the supply tanks, and a recovery tank connected to the recovery channel. The mixture or mixing tank can be alternatively connected to a suction line or to a delivery line.
This device suffers from numerous disadvantages. It requires the use of an air pressure regulator, which must be precise, fast, have no hysteresis so as not to modify the printer operating conditions, have a passage diameter of considerable size at the outlet so as not to lead to an overpressure during ink transfers accompanying a high pump capacity. It does not permit an ink jet droplet speed regulation. It has a manual, precision pressure regulator. It has two other air pressure regulators, which increases to three the number of regulators used. It uses a transfer pump (volume) with a considerable displacement of a unidirectional nature. This non-reversible pump does not make it possible to implement rapidly all the cycles necessary for a printer rinsing or emptying or an ink colour change. It uses a main filter downstream of the accumulator or storage tank, which requires a permanent adjustment of the operating pressure in order to compensate a clogging thereof. Additive addition is a function of the operating conditions and requires a manual setting. The electrical/hydraulic separation is brought about by using solenoid valves, which control pneumatically controlled valves. This relaying principle increases the number of components (cost and reliability aspects). It has components integrated in the interior of a machined unit. It has no temperature sensor. Therefore temperature variations can be interpreted as ink quality variations.
The invention is therefore directed at an ink circuit making it possible to obviate these various disadvantages.
The present invention describes an ink circuit more particularly comprising an ink cartridge, an additive cartridge, a recovery tank, an accumulator or storage tank, a main filter, solenoid valves, an ink transfer pump equipped with a pressure and temperature sensor, which provides information on the operational hydraulic and thermal conditions and an air pressure regulator, said ink circuit being characterized in that it comprises a double face support unit having a hydropneumatic face and an electronic face making it possible to separate the hydraulic, pneumatic and electronic assemblies, all the functional components being fitted outside one or other of the two faces.
Advantageously, the relative arrangement of certain components contributes to an improvement in the overall functionality of the ink circuit. Thus, the air/ink separation is ensured by an arrangement of the air-operating components in the upper part of the circuit and the mainly ink-operating components in the lower part thereof (natural separation by gravity). The pump is also located below the recovery tank and the storage tank, so as to naturally ensure a purging of said pump.
In the storage tank, a first liquid-pressure regulation is assured by the pump, whilst a second air-regulation is assured by means of two solenoid valves, one being located between the storage tank and one or more head pressurizations through gauged orifices and the other between the gauged orifice or orifices and the pressure regulator.
The first solenoid valve makes it possible to inflate or deflate the storage tank independently of the pump.
The second solenoid valve makes it possible to control the head pressurization, said option being directly controlled by the software in order to have a permanent pressurization of the head, said solenoid valve being in the open position (permanent electrical control) and for eliminating pressurization, the control of said solenoid valve being deactivated.
A third solenoid valve makes it possible to control the supply of a venturi tube (vacuum generation). This solenoid valve more particularly makes it possible to stop the vacuum on stopping the ink jet or jets. This in particular prevents any ink quality drift (needless evaporation), which occurs on stopping the ink jet on circuits not having the possibility of stopping vacuum generation.
Advantageously, the pressure sensor, which can be located in the pump, makes it possible to control the driving pressure of the pump. The driving pressure control cycle is controlled by solenoid valves.
The pressure read by the pressure/temperature sensor is then very close to the pressure prevailing in the chamber. This pressure is also very close to the pressure prevailing at the pressure regulator outlet. This sensor then has a pressurestat function and is then used for controlling the presence of the air system or network.
The pressure and temperature sensor makes it possible, during the phase of setting the operating parameters of the machine, to obtain information on the set pressure at the regulator outlet and on the vacuum in the recovery tank. On other prior art circuits, these informations are given by a needle pressure gauge (solely for indicating the regulated or set pressure) and a needle vacuum gauge (solely for indicating the operating vacuum). This sensor makes it possible to avoid the multiplicity of components and gives a more precise and simpler information (the pressure level being read directly on the screen or display of the machine) than needle indicators or gauges. This information can be directly used by software.
Advantageously, the hydraulic and pneumatic links within the circuit take place without using pipes or tubes and without any connection, being directly integrated by moulding into the unit in the form of channels. The hydraulic links with the head are implemented by fast, self-sealing couplings. The air filters are fitted to the unit by a fast fixing system (screwing or bayonet). No pipe is connected to said filters, so that the replacement of these components becomes a simple, clean operation requiring no tool (possibility of manual fitting and dismantling).
Moreover, the accessibility of the ink and additive cartridges and the main filter associated with the use of the reversible pump ensures a rapid colour change.
Advantageously, the ink circuit comprises a double pressure regulation accumulator (by air or liquid). The first regulation functions in liquid by means of the pump and corresponds to the ink supply of the jet, whilst the second regulation functions in air.
This regulation in air in particular makes it possible to relay the liquid regulation when the tanks containing the ink are empty. Thus, use is made of all the ink contained in the machine (including that of the storage tank) prior to the declaration of a blocking fault for the machine. It also ensures the maintaining of a stable pressure in said storage tank throughout the cycle of placing the cartridges under atmospheric pressure. It also ensures the supply of the air pocket of the storage tank without passing via the pump. It also permits a very rapid variation over the entire extent (extending from the vacuum generated by the venturi tube up to the outlet pressure of the regulator) of the pressure prevailing in said storage tank, said rapid and controlled variations of the pressure in the storage tank being used for the stopping and starting cycles of the jet or jets or for carrying out a rapid filling of the storage tank (possibility of placing the storage tank under vacuum). The regulation of the pressure in air of the storage tank is associated with an electrical supply time of the control solenoid valve, whereas the pressure upstream of the solenoid valve is either the atmospheric pressure when the solenoid valve is closed and it is wished to reduce the storage tank pressure, or the regulated pressure present at the outlet of the regulator when the solenoid valve is open and it is wished to increase the storage tank pressure.
Advantageously, the ink circuit comprises a main filter for the ink located between the pump and the storage tank.
Advantageously, the ink circuit comprises a single contactless level detector (intrinsic security by design), a programmable efficiency condenser (function of the ink type, ambient temperature, cycles taking place, etc.) located at the outlet of the recovery tank for condensing and recovering the volatile components of the ink and said condenser can e.g. be based on a Peltier effect cell.
Advantageously, the ink circuit comprises a regulatable venturi tube (vacuum generation) protected by a coalescence filter. The coalescence filter, located at the inlet of the circuit controls and ensures the quality of the air (pollution levels, relative humidity and oil quantity). The purging of said filter is of a permanent nature through a gauged orifice. Such a purging principle involves no moving part, which gives it a reliability level much higher than in existing automatic systems.
Advantageously, the outlets of the filter and venturi tube are located close together, so as to bring about a dilution of the venturi tube discharges.
The electronic and fluidics assemblies are permanently scavenged by an air flow having a quality controlled by the coalescence filter. These scavenging operations create a slight overpressure within the machine, so that there is a high degree of dust protection (e.g. IP6X).
The scavenging of the electronic and fluidics parts remain present when the machine stops. The scavenging operations are only conditioned by the presence of the air system at the filter intake.
The outlets of the coalescence filter and the venturi tube are connected to the same component T, whose third orifice is connected to the outside of the machine, which makes it possible to dilute the solvent vapours discharged to the outside, so that the pollution level is very low and well under accepted levels. In a constructional variant, the same effect can be obtained without connecting the two outlets (filter and venturi tube), but instead by individually connecting them in the lower part of the machine. The two connections would then be close to one another.
Advantageously, the ink and additive cartridges are tight and maintained at a pressure close to atmospheric pressure by the storage tank air, as a result of an adapted cycle of several solenoid valves, the operation being controlled by the pressure sensor.
The invention also relates to an ink jet machine using such an ink circuit and a conditioning machine or conveyor using such an ink circuit.
The ink circuit according to the invention gives rise to the following advantages.
The implementation of an autonomous electro-hydropneumatic circuit integrating all the sensors and actuators necessary for its operation and the associated control electronics. The ink circuit constitutes an autonomous assembly which can be likened to an automaton controlled by a series, bidirectional data link. This architecture makes it possible to install and test in an autonomous manner the complete circuit and also use the latter as a component in specific applications (e.g. multicolour printing).
The simplicity and very good separation of the assemblies (hydraulic, pneumatic, electronic), with two faces, including a hydropneumatic face and an electronic face. This separation in the arrangement of the components makes it possible to very easily separate or distinguish the fluidics zone (hydraulic side) and the electronic zone, with a clear advantage for the operating safety.
The implementation of a double face hydraulic circuit with ease of manufacture, access and maintenance. All the functional components (filters, venturi tube, pump, solenoid valves, pressure and level sensors, condenser, etc.) are installed outside one or other of the faces and are consequently rapidly accessible.
The implementation of a closed circuit (isolated from the ambient air).
When the machine stops, the circuit is isolated from the outside, which avoids the drying phenomena associated with air/ink exchanges.
The use of a numerically controlled air pressure regulator.
The integration of a pressure and temperature sensor in the ink transfer pump.
The use of a solvent recovery means (e.g. condenser with Peltier effect cell) with a programmable efficiency.
The particular position of the main filter makes it possible to envisage an optimized regulation of the ink quality and the clogging of the filter does not influence the ink quality, as well as an automated determination of the filter change.
The use of a coalescence filter for protecting the venturi tube, which is a sensitive element.
The determination of the ink levels in the different volumes by the pump.
The use of an entirely pneumatically controlled ink transfer pump, said reversible pump ensuring all the bidirectional liquid exchanges between all its neighbours (cartridges and tanks).
A very low thermal balance linked with the fact that the xe2x80x9cmotorxe2x80x9d of the printer is the pressurized air of the factory network, which makes it possible to predict a very small internal temperature rise ( less than 5xc2x0 C.).
Unlike in the case of the previously described prior art device, the ink circuit according to the invention makes it possible:
to continuously regulate the ink jet droplet speed,
electronically regulate the pressure, with a permanent servo-control,
transfer the liquid in any random condition, the pump of the circuit according to the invention having the functions of transferring liquid between two tanks, stirring and agitating a tank, measuring the transferred volume, measuring the pressure (vacuum) in a tank, measuring the level in a tank, measurement more particularly taking place of the air quantity in the pressurized tank (accumulator), knowing the total volume thereof and the ink volume and in particular ink level in said accumulator is deduced by subtraction and control of the pressure of the network,
to decorrelate the clogging level of the main filter located between the pump and the storage tank from the viscosity of the ink, the pressure being automatically compensated and a dynamic measurement (calculation of the transfer energy in the storage tank) provides the information as to whether the filter is clogged,
of no longer having the additive addition dependent on the operating conditions (everything takes place through the pump, which has a known chamber volume),
to implement the electrical/hydraulic separation within the solenoid valves using separating membranes or diaphragms, which bring about a physical separation between the electrical part and the hydraulic part, so that the solenoid valves are directly controlled,
to use a double face circuit with two isolated, pressurized compartments, the maintenance of the first level taking place solely in the hydraulic component at the front of the machine,
to use a pressure and temperature sensor integrated into the pump, so that it is possible to control the ink quality,
to use a contactless level detector placed on the wall of the recovery tank giving information (analog output or several level values) on the level and therefore volume of the ink contained in the recovery tank,
to use the knowledge of the ink volumes contained in the recovery tank, storage tank and pump chamber so as to be able to entirely control the additive concentration corrections necessary for maintaining the ink quality,
to use a condenser (e.g. Peltier effect type), whose efficiency can be controlled as a function of the temperature in accordance with the operating characteristics, so as to discharge less vapours of the volatile components of the ink.
These characteristics of the circuit according to the invention make it possible:
to reduce the number of components (pipes, couplings, small support units, etc.),
to have a compact circuit,
to directly integrate with the support unit the tanks (buffer, storage, condenser),
to reduce the costs to a significant extent by directly obtaining by moulding the support unit for all the components,
to adequately separate the electronic and hydropneumatic parts (important for safety standards),
to limit the first level maintenance interventions to a single face of the circuit (front face directly accessible by the operator),
to simplify maintenance (all the components being accessible from the outside without any prior dismantling),
to obtain an autonomous ink circuit integratable into units other than ink jet printers, all that is required consists of the electrical power, compressed air and appropriate controls (through the series control link) in order to make the circuit functionxe2x80x94said autonomy concept making it possible to simplify manufacture (complete integration test in air based on a computer).